Identification of a communication network is made in a digital radio communication system including a plurality of base station apparatuses that perform radio communications with at least one communication terminal apparatus. This communication network identification is made, for example, in the following cases:
(1) To check whether a network is connectable or not prior to authentication, etc. after power of a communication terminal is turned on and before starting a communication with a base station (AP) (at the time of so-called association)
(2) To verify operator and services supported, etc. at handover destination
Identification of a communication network is made using a network identifier (e.g., network ID, hereinafter abbreviated as “NET-ID”). For this NET-ID, several bits of CCH (Broadcast Control CHannel) are used. A communication network is made identifiable by assigning this NET-ID to each communication network.
In general, 4 bits of BCCH are used as a NET-ID, making 16 types of communication network identifiable. This NET-ID is determined using random numbers when a communication network is set up.
However, in Japan, 4 frequencies are assigned as a 5-GHz band of radio communication. When there are many adjacent private networks in office buildings in a downtown area or when there is a plurality of public networks of different service types, etc., there can be many communication networks in narrow bands of a specific region.
Considering these situations, it is quite difficult to identify a communication network using a 4-bit NET-ID. Therefore, when many communication networks coexist, it may be quite difficult to identify communication networks according to the conventional method.